Originally Posted by
Chombi
Remember, butted tubing means it's thicker at the ends and not the middle, so you cannot just drop items down the tube and expect it to stop and jamb against a section in the middle. The thinner wall section at the middle will just let it drop down towards the BB shell or lower butted section, much lower than the few inches down the OP noted on his PX10. My 80's Peugeot PSV does not have this plug in it. I figure that they used to do it back then for some obscure "French" bike building design logic/purpose.........which is not surprising these days when looking back at older French bike frame
construction and component design.
Chombi
84 Peugeot PSV
85(?) Vitus Plus Carbone 7
Except that most seat tubes, including those used by Reynolds, are
single butted, meaning there is no thick section at the top. The tube diameter is the same all the way down to just above the bottom bracket. So, if you put a light interference fit plug in the seat tube, you could drive it down to any depth, until it hit the butt, just above the BB shell.